Misfire mystery

[Fullraceflathead]

Before you tear into the valves I would try a new condenser.

[Fairlane514]

I did that already, Echlin FA-82......

Not say its not a faulty new one.....it runs the same with the old condenser versus the new one.

Its the modern style points and condenser with the NuRex plate etc

[mcgarrett]

Originally Posted by Fairlane514

Drove it some today, to a fellow Model A owner about 10 miles away.

It seems to have plenty of power and cruises well, I dont really notice the misfire when driving and underload. I come to a stop, it stays running. A little clutch chatter on take off (another issue to address), but upshifts fine.

No real difference as of yet.....

The other owner does have an aluminum head he wants to sell, I will post that separately. Cant ID it....Has the letter R with two circles around it cast right near the distributor hole.

The "R" cast into the head, possible it could be a Ricardo head?

[Fairlane514]

I have no clue, research doesnt come up with much.

Riley maybe? May be a stock replacement head, but why aluminum....

[Fairlane514]

https://www.fordbarn.com/forum/attac...1&d=1706712884

[Big hammer]

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Man that head needs a good glass bead blasting ,it’s probably a Riley !?

[Rob Doe]

If you can feel the misfire from the driver's seat, watch the ammeter for any slight twitch. As described, your car is wired correctly as per the 1929, Nov. service bulletin. A steady or intermittent, unintended ground between the pos + post of your coil and the ignition points likely would affect the reading at the ammeter. With the engine not running, a steady, unintended ground should show a small neg - reading. The primary windings of the coil prevent the safety fuse from blowing. I've not yet experienced such an issue myself.

I'm not certain whether or not you could see the single intermittent misfire, but if you can feel it from the seat and see a coinciding, small twitch in the ammeter, it would indicate the location of the problem.

It is easy to bypass the switch and the heavy cable to the distributor with the modern upper plate installed. Unhook the red pos + wire at the coil and the wire from the lower plate at the side of the upper plate. Insulate the ends of the wires removed. Run the jumper wire from the coil pos + to the side of the upper plate. Use minimum of 16 gauge wire.

Pull the safety fuse to shutdown the engine.

[Rob Doe]

Check the rivets and the insulators on the lower (and upper??) plates for tightness. A club member's distributor was recently found to have loose rivets, which allowed an intermittent issue.

Marshal Daut posted some time ago that he had, on a couple occasions, found that a reproduction terminal box had it's studs loosen. This allowed the screw heads of the studs to get close enough to the firewall to jump a spark. The heads of the terminal box studs of an original terminal box are covered. The repro's are not, but they should be.

[Fairlane514]

I did check for continuity between the terminal box studs and the firewall, none found.

When I had the distributor apart and did check the rivets, they are tight.....all that stuff looks pretty new. The shaft is solid without wobble and very little end play as well.

I can try the bypass test.

I have tried posting the video of my vacuum gauge, but it states "no security button" or something to that effect.

[Fairlane514]

Well......nothing simple so far, tried what has been suggested, which I really appreciate.

I think I will drive it more and see if it clears up.

I do want to upgrade to a high compression head, so when its apart I will check valve guides, springs etc...

[katy]

Originally Posted by Fairlane514

I think I will drive it more and see if it clears up.

That may be what it needs, some good serious running.

[Fairlane514]

Thinking out loud here....

Worn distributor gear?

[Marshall V. Daut]

'Sounds as if you've covered most bases, but still no luck finding the source of the misfire? It's there someplace. These cars didn't leave the factory with misfires. You'll find it. I'm leaning towards a weak or broken valve spring, too, since you have eliminated most electrical and carburetor-related misfire causes. TBD...
I didn't see it mentioned, but do you have a water temperature or oil pressure gauge with a light bulb for gauge face illumination? And if so, where does it get its power? I know this sounds weird, but if you do have one or both of these aftermarket gauges, disconnect the wire for the light from its power source. Why? Years ago I chased a misfire in a 1931 Coupe that I had rebuilt for a doctor friend a decade before in Phoenix. He had died in the meantime and his car showed up locally for sale. My friend had added a water temperature gauge or oil pressure gauge (I don't recall which) since I had restored the car. The car showed up with a definite miss under power demands, but the engine idled nicely. I jumped through all the hoops you have, but still couldn't find the source of the misfire.
Eventually, I disconnected the gauge's light bulb wire to completely remove the instrument panel to check for shorts. The gauge was located in a bracket beneath the panel, so it went with the now-removed panel. When I re-installed the instrument panel after finding nothing wrong with the connections behind it, I neglected to hook up the gauge's light wire. Starting the engine and test driving it for the millionth time - behold! The misfire was gone!!! I noticed the gauge's wire dangling beneath the gas tank, so I reconnected it to the terminal box's hot stud where it had been. Guess what! The misfire was back! Disconnecting the wire again, the misfire went away. I deduced that for some reason, that light socket was causing the engine to misfire by interfering with the ignition system via the terminal box stud. Maybe that's what is causing your misfire. If you don't have an auxiliary water temperature or oil pressure gauge with a light bulb, ignore what I just spent the last 10 minutes typing. But maybe this information will help someone else with a similar problem.
Marshall

[Synchro909]

Originally Posted by Marshall V. Daut

'Sounds as if you've covered most bases, but still no luck finding the source of the misfire? It's there someplace. These cars didn't leave the factory with misfires. You'll find it. I'm leaning towards a weak or broken valve spring, too, since you have eliminated most electrical and carburettor-related misfire causes. TBD...
I didn't see it mentioned, but do you have a water temperature or oil pressure gauge with a light bulb for gauge face illumination? And if so, where does it get its power? I know this sounds weird, but if you do have one or both of these aftermarket gauges, disconnect the wire for the light from its power source. Why? Years ago I chased a misfire in a 1931 Coupe that I had rebuilt for a doctor friend a decade before in Phoenix. He had died in the meantime and his car showed up locally for sale. My friend had added a water temperature gauge or oil pressure gauge (I don't recall which) since I had restored the car. The car showed up with a definite miss under power demands, but the engine idled nicely. I jumped through all the hoops you have, but still couldn't find the source of the misfire.
Eventually, I disconnected the gauge's light bulb wire to completely remove the instrument panel to check for shorts. The gauge was located in a bracket beneath the panel, so it went with the now-removed panel. When I re-installed the instrument panel after finding nothing wrong with the connections behind it, I neglected to hook up the gauge's light wire. Starting the engine and test driving it for the millionth time - behold! The misfire was gone!!! I noticed the gauge's wire dangling beneath the gas tank, so I reconnected it to the terminal box's hot stud where it had been. Guess what! The misfire was back! Disconnecting the wire again, the misfire went away. I deduced that for some reason, that light socket was causing the engine to misfire by interfering with the ignition system via the terminal box stud. Maybe that's what is causing your misfire. If you don't have an auxiliary water temperature or oil pressure gauge with a light bulb, ignore what I just spent the last 10 minutes typing. But maybe this information will help someone else with a similar problem.
Marshall

Wow, I don't think anybody would have found that one without the sort of luck you had. I am chasing a miss in a friend's car at the moment and your finding might help. He has a temperature gauge with the light permanently on. I don't know yet where it is connected but I bet it is behind the instrument panel. I plan on connecting it to the tail light circuit so that it is only on when the lights are on and on regardless of high or low beam or parking lights.
FWIW, The symptoms on my friend's engine would indicate a vacuum leak. I found and fixed one but the miss was only reduced, not fixed. At some point, someone has fitted a PCV valve and a hose from the oil filler cap to the inlet manifold. Disconnecting that cured the problem but allowed oil to literally pour out of the back of the motor. Next step is to drop the sump and check out the rear bearing/oil slinger etc area. I suspect something is so wrong there that air is entering the motor, travelling through the crank case until it is sucked into the manifold, causing it to run lean.

[Fairlane514]

No , I dont have any gauges.....Im going to drive it some more, and then pull the valve cover when I get some time from my other 4 projects.

Thanks to everyone for the help.

I will post what I find

[Fairlane514]

Got the head off today. Cylinders look pretty good, minimal ridge at top, barely feel it.

Valves need lapping, exhaust have baked on "sand" like coating.

New springs are shorter and thicker wire by about .015 thousandths. Look to measure 50 pounds pressure at 2.250 length. Old springs were 10 pounds less at same length.

[nkaminar]

You have gone through the ignition system from head to toe so I am going to say it is something else. I found that the jets in my carburetor were not drilled correctly so you may want to go through the carburetor and "blue print" it, meaning to make sure that everything is as designed. You can make a rig to flow test the jets for have them flow tested.

It is normal for a slight miss while not under load. The engine is really designed for running at its normal rpm and load and not at an idle or under no load. That is probably not the case here but something to keep in mind.

To manually set the ignition, search for the knee. With the car in neutral, use the hand throttle to set the engine at a fast idle. Start with the ignition lever in a slightly retarded position and increase the advance one notch at a time. The engine rpm should come up with each notch. If not, start with the ignition more retarded. At some position the engine rpm will not increase. That is the knee. Retard the ignition one notch and either remember that position or mark it. That is where you should be driving the car most of the time. You can retard the ignition one notch if under heavy load, especially at lower rpm. You can also advance the ignition one notch if you are cruising down the highway at a fairly fast clip but not much throttle. You can also search for the knee while driving the car on a level road while using the hand throttle.

Lower compression engines (stock) are more sensitive to ignition timing so if that is the case here, you may want to use more retard and advance under different driving conditions.

[Fairlane514]

Removed the valves, too them to a friends machine shop for refacing.

2 are slightly bent, the rest are on the edge of usable.....

Im going to get a new set.

[nkaminar]

New valves will help a lot. Buy a seat cutter or have someone cut the seats. Lightly lap the valves until there is a uniform grey ring where they seat. Make sure the guides are good. Quickly pull out the new valves with your finger on the bottom of the guides. There should be pop when the valves pull out of the guides.

[Fairlane514]

I have new guides